In recent years, optical disks, optical cards and optical tapes and the like have been proposed and developed as media for optically recording information. Of these, optical disks have come in for particular attention as media that are capable of recording and reproducing information, both in large volumes and at high density. A phase change-type optical disk is one type of rewritable optical disk. In order to obtain the desired thermal and optical characteristics in phase change-type optical disks, it is common to use a multi-layered film configuration in which layers such as dielectric layers and reflecting layers are added onto the recording layer. The recording layer that is used in the phase change-type optical disk is either amorphous or crystalline, depending on the heating and cooling conditions caused by the laser light, and is reversible between the amorphous and crystalline states. The optical indices (refractive index and attenuation co-efficient) of the recording layer differ between the amorphous and crystalline states. In the phase change-type optical disk, the two states are selectively formed on the recording film in response to an information signal, and the optical changes (changes in transmittance or reflectance) that occur as a result are utilized to record and reproduce the information signal.
In order to obtain the two states, the information signal is recorded by a method such as described below. A laser light (power level Pp) that is focused by the optical head is irradiated onto the recording film of the optical disk in pulses (known as recording pulses) to raise the temperature of the recording film. When the temperature exceeds the melting temperature, the recording film melts, and after the passage of the laser light, the melted portion rapidly cools to become an amorphous recording mark (also known as a mark). It should be noted that the power level Pp is known as the peak power. Furthermore, when the light, whose intensity is of a level that raises the temperature of the recording film to more than the crystallizing temperature and less than the melting temperature, is focused and emitted by a laser light (power level Pb, where Pb<Pp) the irradiated portion of the recording film is crystallized. It should be noted that the power level Pb is known as the bias power. Furthermore, the peak power and the bias power more generally are referred to as recording power.
In this manner, a recording pattern of recording marks, which are created from amorphous regions that correspond to the recording data signal, and non-mark portions (also known as “spaces”), which are made of crystalline regions, is formed on a track of the optical disk. Thus, an information signal can be reproduced, utilizing the difference in optical characteristics between the crystalline regions and the amorphous regions.
Furthermore in recent years, use of the mark edge recording method (also known as PWM recording) has increased, replacing the mark position recording method (also known as PPM recording). As opposed to mark position recording, in which information is only held in the position of the recording mark itself, in mark edge recording, information is held in both the forward and back end of the edge of the recording mark, and thus it is advantageous for increasing the recording line density.
In the case of mark edge recording, the recording pulse during recording of a long mark is divided into a sequence of a plurality of recording pulses (these are known as multi pulses), and a recording method is used in which the width of the front pulse (known as the front end pulse) is made larger than the width of the middle pulses or the width of the last pulse (known as the back end pulse). Considering the influence of excess heat that is transmitted from the front portion of the mark, this is in order to lessen the distortion of the recording mark shape, and to record a more accurate mark by reducing the heat applied to the recording film when recording the rear portion of the mark to less than that which is applied when recording the front portion of the mark.
Coincidentally, in the case of the mark edge recording method, differences in thermal characteristics of optical disks affect the shape of the recording mark itself, and the degree of thermal interference between recording marks. That is to say, even if recorded by the same recording pulse waveform, the shape of the recording mark that is formed will differ between disks. As a result, the edge of the recording mark may be offset from the ideal position, depending on the disk, and the quality of the signal that is reproduced may drop. Because of this, methods have been proposed with which a recording mark can be recorded at an ideal edge position by optimally correcting the recording power, front end pulse edge position or back end pulse edge position for any disk.
As a method for correcting the front end pulse edge position or the back end pulse edge position, a method has been proposed in which combinations of code lengths that correspond to recording marks (known as recording code lengths), and code lengths that correspond to spaces before or after the recording marks (known respectively as pre-code length and post-code length) are provided in a correction table, and the front end pulse edge position and the back end pulse edge position are corrected according to correction values for the combinations in the correction table (known as correction table elements).
Furthermore, as a test recording method for correcting the front end pulse edge position and the back end pulse edge position, a method that corrects the front end pulse edge position or the back end pulse edge position has been disclosed in which before recording an actual information signal, a test pattern that has a specific period (known as a test pattern) is recorded, after which the test signal that was recorded is reproduced, and the front end pulse edge position and back end pulse edge position are corrected according to the amount of offset of the recording mark edge determined by measuring the reproduced signal.
It should be noted that the conventional methods described above are disclosed in, for example, Patent Document 1 given below.
Patent Document 1: WO 00/57408.
However, in the conventional methods described above, the correction table for optical disks that have different recording characteristics and recording conditions is always determined via a succession of identical test recording steps. Thus, if, for example, the thermal interference of an optical disk is small, and it is not necessary to correct the front end pulse edge position and the back end pulse edge position for each element of the correction table in order to obtain sufficient reproduction signal quality, then by going through what is effectively an unnecessary test recording step, the result is that there is a problem in that excessive time is taken for the recording and reproduction apparatus to come to a state in which it is actually capable of recording an information signal.